Chemical-to-electrical energy conversion devices, especially PEM fuel cells, are of great interest as efficient, non-polluting power sources for automotive applications, and also for stationary applications such as distributed power sources for buildings and houses as well as portable power generation for consumer electronic devices. A major barrier to commercial application of this technology is the cost of the devices.
A key component of the fuel cell design (and for electrochemical power generation devices in general, such as some battery designs) is the well-known bipolar plate, which serves to separate fuel and oxidant and to connect the cathode of one cell to the anode of the adjacent cell in a stacked series. The cost of the machined graphite bipolar plates in PEM fuel cells accounts for as much as 60% of the overall fuel cell stack costs. Metallic bipolar plates offer the potential for significantly lower cost since they can be formed by readily available and inexpensive conventional metal forming processes.
Low cost graphite and carbon fiber net shape composites are under development to replace the machined graphite plates. However, gas permeability and strength issues require the composites to have a greater thickness than a corresponding metallic bipolar plate, which increases both volume and weight, making them less desirable for many applications where power density is important.
A well-known drawback of metallic bipolar plates is that they generally exhibit inadequate corrosion resistance, which leads to high electrical resistance and/or PEM contamination, degrading fuel cell performance to unacceptable levels. Corrosion-resistant coatings have been applied to metallic bipolar plates, but surface defects therein have limited the success thereof.